1. Field of the Invention
The present invention relates to copolyesters, processes for producing the same and aromatic triols used for the production of the same; and, further, to a process for producing molded articles therefrom and molded articles obtained from said process. The copolyesters of the present invention have a high melt viscosity and have the non-Newtonian characteristics of exhibiting low viscosity at high shear rates and high viscosity at low shear rates, and are hence applicable to various molding processes, in particular to extrusion blow molding to produce hollow molded articles.
2. Description of the Prior Art
Resins of polyesters such as polyethylene terephthalate are excellent in various features such as transparency, mechanical properties, gas barrier properties and flavor barrier properties and, cause little worry with respect to residual monomers and toxic additives, in hygiene and safety, when molded into shaped articles. The resins have therefore become widely used in recent years, while replacing polyvinyl chloride resin, for hollow containers to be filled with juices, soft drinks, relishes, oil, cosmetics, cleansers and similar items.
Two representative processes for producing hollow shaped articles such as plastic containers are extrusion blow molding which comprises extruding a melt plasticized resin through a die-orifice into a cylindrical parison and, while holding the parison as it is still softened, blowing a fluid such as air into the parison; and injection blow molding which comprises injecting a melted resin into a die to mold a closed parison (preforms) once and, after inserting it into a blow die, blowing a fluid such as air into the preforms.
Of the above processes, the former, i.e., extrusion blow molding, is simpler than the latter, i.e., injection blow molding, and requires no complex techniques to prepare dies and for molding, and hence requires only the cost of equipment and die preparation. Extrusion blow molding is therefore suitable for multiple-product-small-quantity production and, further, has the advantage of being capable of producing thin, thick or large articles and complex-shaped articles having a knob or like irregular fittings.
Various attempts have therefore been made to conduct extrusion blow molding with general-purpose polyesters, such as polyethylene terephthalate and polybutylene terephthalate. However, general-purpose polyesters generally have low melt viscosity, so that, when they are extrusion blow molded, the parisons extruded markedly sag (drawdown) and become difficult to shape. In addition, crystallization tends to occur on blowing after extrusion, thereby reducing the transparency or shapability. These disadvantages of conventional polyesters as caused by their low melt viscosity and ready crystallizability are more marked when they are extrusion blow molded into long parisons having a length of, generally, 20 cm or more, which is required for producing large-size hollow molded shaped articles. As a result, it becomes very difficult to obtain shaped articles, in particular large ones, having a uniform shape and size and, at the same time, good transparency from conventional polyesters by extrusion blow molding.
For the above reason, in conducting extrusion blow molding, there have been used polyvinyl chloride and polyolefin resins, which have high melt viscosity and cause the extruded parisons in a melted condition to sag only to a small extent. However, extrusion blow molded articles from polyvinyl chloride resin have some hygiene or safety problems with respect to elution of toxic additives such as plasticizers and metal-containing stabilizers and, further, in that incineration of waste of the molded articles generates toxic gases. Their use has therefore been decreasing in Europe and other areas. Extrusion blow molding with polyolefins such as polyethylene results in shaped articles becoming white turbid due to crystals, so that the articles tend to have poor transparency and appearance.
In view of the above, several proposals with respect to polyester resins applicable to extrusion blow molding have therefore been made, including:
1 U.S. Pat. No. 4,161,579, 4,219,527, 4,234,708 and 4,182,841 and Japanese Patent Application Laid-open No. 92730/1980 disclose a process for producing polyester applicable to extrusion blow molding, which comprises subjecting a dicarboxylic acid component such as terephthalic acid or ester-forming derivatives thereof and a diol component such as ethylene glycol to esterification or transesterification to obtain a low-polymerization-degree compound, reacting with the compound a conventional crosslinking agent such as trimethylolpropane, pentaerythritol or trimellitic acid to prepare a prepolymer and subjecting the prepolymer to solid phase polymerization; PA1 2 A process which comprises, on producing polyethylene terephthalate, polybutylene terephthalate or the like, copolymerizing isophthalic acid or cyclohexane dimethanol is known; and PA1 3 EP 0532943A1 discloses a process for producing modified polyesters, which comprises adding, on producing polyethylene terephthalate, polybutylene terephthalate or the like, an ethylene oxide adduct of bisphenol A. PA1 (i) diol units consisting essentially of ethylene glycol units and dicarboxylic acid units consisting essentially of terephthalic acid units, PA1 (ii) at least one group of triol units selected from the group consisting of: PA1 (i) diol units consisting essentially of ethylene glycol units and dicarboxylic acid units consisting essentially of terephthalic acid units, said copolyester further comprising: PA1 (ii) at least one group of diol units selected from the group consisting of: PA1 (iii) at least one group of triol units selected from the group consisting of: PA1 (1) a dicarboxylic acid component consisting essentially of terephthalic acid or ester-forming derivatives thereof; PA1 (2) a diol component consisting essentially of ethylene glycol; and PA1 (3) a triol component containing at least one triol selected from the group consisting of: PA1 (a) a triol represented by the following formula (V) ##STR8## wherein A is a group represented by formula --CH.sub.2 CH.sub.2 -- or formula --CH(CH.sub.3)CH.sub.2 --, B is a divalent hydrocarbon group, a carbonyl group, a sulfonyl group, an oxygen atom or a direct bond (-), and p, q and r are each, independently, an integer of 1 to 8; and PA1 (b) a triol represented by the following formula (VI) ##STR9## wherein A is a group represented by formula --CH.sub.2 CH.sub.2 -- or formula --CH(CH.sub.3)CH.sub.2 --, and s, t and u are each, independently, an integer of 1 to 8, PA1 in an amount of about 0.01 to 1 mole % based on the sum of the moles of total diol and said triol components; PA1 melt polycondensing the obtained reaction product to form a polyester prepolymer; and PA1 subjecting the polyester prepolymer to solid phase polymerization. PA1 (1) a dicarboxylic acid component consisting essentially of terephthalic acid or ester-forming derivatives thereof; PA1 (2) a diol component consisting essentially of ethylene glycol and containing at least one diol selected from the group consisting of: PA1 and p, q and r are each, independently, an integer of 1 to 8; PA1 and an aromatic triol component represented by the following formula (VI) ##STR13## wherein A is a group represented by formula --CH.sub.2 CH.sub.2 -- or formula --CH(CH.sub.3)CH.sub.2 -- and s, t and u are each, independently, an integer of 1 to 8. PA1 1 diol units (III) and triol units (I), PA1 2 diol units (III) and triol units (II), PA1 3 diol units (IV) and triol units (I), PA1 4 diol units (IV) and triol units (II), PA1 5 diol units (III), diol units (IV) and triol units (I), PA1 6 diol units (III), diol units (IV) and triol units (II), PA1 7 diol units (III), triol units (I) and triol units (II), PA1 8 diol units (IV), triol units (I) and triol units (II), PA1 9 diol units (III), diol units (IV), triol units (I) and triol units (II). PA1 (1) a dicarboxylic acid component consisting essentially of terephthalic acid or ester-forming derivatives thereof, PA1 (2) a diol component consisting essentially of ethylene glycol; or a diol component comprising ethylene glycol and a diol component (VII) represented by the above formula (VII) and/or a diol component (VIII) represented by the above formula (VIII) in an amount of about 1 to 15 mole % based on the sum of the moles of total diol and triol components described in (3) below, and PA1 (3) a triol component containing a triol component (V) represented by the formula (V) and/or a triol component (VI) represented by the formula (VI), in an amount of about 0.01 to 1 mole % based on the sum of the moles of total diol and triol components; PA1 to form a polyester prepolymer and then solid phase polymerizing the polyester prepolymer.
However, polyesters obtained by the above process 1 give extrusion blow molded articles having no transparency with marked whitening due to formation of spherulites resulting from increased rate of crystallization. Further, in some cases, gels generate which are caused by crosslinking and cause the resulting shaped articles to contain agglomerates, thereby marring their appearance.
The present inventors have, based on the above known art 2, produced polyethylene terephthalate-based copolymers with the melting point decreased, by copolymerizing isophthalic acid or cyclohexane dimethanol and attempted to carry out extrusion blow molding with these copolyesters while setting the melt extrusion temperature at a lower temperature than before. However, because of the melt viscosity being not sufficiently high at the extrusion temperature, the parisons extruded upon extrusion molding sagged markedly and were difficult to shape, so that the extrusion blow molding operation could not be run smoothly. Furthermore, with the copolyesters copolymerized with isophthalic acid or cyclohexane dimethanol obtained by the prior art 2, solid phase polymerization could not be conducted or, if ever conducted, proceeded too slowly to achieve a sufficiently high degree of polymerization. As a result, shaped articles prepared from these copolyesters had a large dispersion of thickness and poor transparency.
The present inventors also conducted a follow-up experiment with the known art copolyester of the above 3, copolymerized with an ethylene oxide adduct of bisphenol A, to find that its extrusion blow moldability was not sufficient.
The present inventors have also attempted, separate from the known art of above 1 through 3, to produce by solid phase polymerization a polyethylene terephthalate having a high degree of polymerization. However, it was found that the rate of the solid phase polymerization was very low, so that it was impossible to produce, in a short period of time and efficiently, a polyethylene terephthalate having a sufficiently high degree of polymerization and melt viscosity suitable for extrusion blow molding and like processes. This method is hence not applicable in practice from the viewpoint of productivity.
Accordingly, an object of the present invention is to provide a polyester having excellent melt moldability with high melt viscosity, in particular excellent extrusion blow moldability, which can yield, when extrusion blow molded, an extruded parison causing no severe drawdown, and shaped articles having desired shape and size, at high precision and smoothly.
Another object of the present invention is to provide a polyester which can give smoothly, on melt molding, in particular on extrusion blow molding, shaped articles having excellent transparency and heat resistance.
A further object of the present invention is to provide a process for producing, in a short period time and at high productivity, polyesters having the above excellent features.
A still further object of the present invention is to provide a process for producing shaped articles from the above polyesters having excellent features by melt molding, in particular extrusion blow molding and, also to provide shaped articles obtained therefrom.
A still further object of the present invention is to provide an aromatic triol which does not form gel-like agglomerates and has a large effect on increasing the rate of polymerization, and is hence useful as a crosslinking agent and a resin-modifying agent.